Rapid pyrolysis of biomass is a thermal treatment process in the absence of air, which produces char, liquid, and gaseous products. During rapid pyrolysis, the pyrolysis temperatures range from 450° C. to 600° C. and vapor residence times are less than one second to five seconds. In a typical reactor for rapid pyrolysis, a cyclone is used at the termination of the riser reactor to separate sand and char from other pyrolysis products. However, the particle size distribution and density of the char is such that not all of it can be separated by the cyclone. Consequently, the pyrolysis oil product typically contains 0.5 to 4% solids as char.
One of the applications of pyrolysis fuel is combustion in stationary diesel engines. However, stationary diesel engines typically cannot tolerate solids with diameters greater than 5 microns. Because a large percentage of char particles remaining in pyrolysis fuel after pyrolysis have dimensions exceeding 5 microns, the char must typically be removed from the pyrolysis fuel before combustion, often by filtration or by centrifugation.
However, the char has a significant heating value (typically 32 MJ/kg compared to 15 to 20 MJ/kg for the pyrolysis oil), and its removal reduces the heating value of the pyrolysis fuel. Further, because the char cannot be removed without entraining some of the pyrolysis oil in the filter cake or the centrifuge sediment, the char removal process also results in a loss of some pyrolysis oil, typically 3 to 10% of the pre-separation volume of oil.
Accordingly, it is desirable to provide methods for processing pyrolysis fuel, and processed pyrolysis fuel, for use in stationary diesel engines. Further, it is desirable to provide fuel processing methods and fuels that retain the high heating value of the char without causing damage to a diesel engine during combustion. Also, it is desirable to eliminate the loss of pyrolysis oils due to the removal of solids during pyrolysis fuel processing. Further, it is desirable to provide fuel processing methods and fuels with char particles of reduced size. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.